Adipic acid is an important intermediate for the production of nylon. Commercial methods for producing dicarboxylic acids generally involve oxidizing naphthenes, cycloaliphatic ketones or cycloaliphatic alcohols with nitric acid in the presence of metal oxidation catalysts.
In the case of adipic acid, specific feed materials such as cyclohexane, cyclohexanol and/or cyclohexanone in admixture with nitric acid are heated at about 40.degree.-140.degree. C. in the presence of a catalyst. The resultant oxidation reaction product comprises adipic acid together with small amounts of monocarboxylic acids and dicarboxylic acids and other organic components in admixture with nitric acid and catalyst components. A substantial quantity of the adipic acid product is recovered by cooling the solution and filtering off the crystallized adipic acid. Oxidation methods of adipic acid production are described in U.S. Pat. Nos. 2,439,513; 2,557,281; 2,719,566; 2,840,607; 2,971,010; 3,338,959; and references cited therein.
In a process involving nitric acid oxidation of cyclohexanol and/or cyclohexanone, economically significant amounts of succinic acid and glutaric acid are formed as byproducts in admixture with the adipic acid. After the major portion of the adipic acid is separated by crystallization and filtration, the filtrate mother liquor contains some adipic acid, as well as succinic acid, glutaric acid, nitric acid and metal catalyst values.
Usually this filtrate has been treated as a waste stream. Because of environmental and economic considerations, there has been continuing research effort to develop methods for recovering the valuable and reusable organic and inorganic components of the said filtrate waste byproduct stream.
U.S. Pat. No. 3,726,888 describes a process for the separation and recovery of the components contained in the filtrate waste byproduct stream of an adipic acid manufacturing plant. The filtrate stream comprises a mixture of adipic acid, glutaric acid, succinic acid, metal catalyst values and nitric acid. The separation and recovery process involves contacting the filtrate with alkanol, and extracting with a water-immiscible organic solvent to provide an organic phase containing the formed esters, and to provide an aqueous phase containing the nitric acid and metal catalyst values. Each of the phases is fractionated to separate the mixtures into useful components.
U.S. Pat. Nos. 4,076,948 and 4,082,788 describe processing improvements which are adapted to overcome some of the difficulties characteristic of the byproduct separation and recovery technology disclosed in the above recited U.S. Pat. No. 3,726,888. There remains a need for further improvements in this kind of byproduct separation and recovery technology.
Accordingly, it is an object of this invention to provide an improved process for the recovery of organic acids from dilute aqueous solutions.
It is a further object of this invention to provide an improved process for the separation and recovery of dicarboxylic acids and other valuable components contained in a filtrate byproduct stream derived from an adipic acid manufacturing operation involving nitric acid oxidation of cyclohexanol and/or cyclohexanone.
Other objects and advantages of the present invention shall become apparent from the accompanying description and exemplary data.